a) Field of the Invention
This invention relates to a solidifying material for cell or battery (hereinafter collectively called xe2x80x9ccellxe2x80x9d) electrolyte solution and a cell comprising the solidifying material as a constituent element. The term xe2x80x9ccell electrolyte solutionxe2x80x9d may hereinafter be referred to simply as an xe2x80x9celectrolyte solutionxe2x80x9d, and the term xe2x80x9csolidifying material for an electrolyte solutionxe2x80x9d may hereinafter be referred to simply as xe2x80x9csolidifying materialxe2x80x9d.
b) Description of the Related Art
As a cell electrolyte is conventionally in a liquid form, it is sealed in a case from the standpoint of safety. To safely hold the electrolyte solution over a long time, the case is required to be strongly built. As a result, it has heretofore been difficult to form a cell into a thin structure. It has recently been proposed to have an electrolyte solution absorbed in a high molecular substance such that the electrolyte is solidified. This approach is expected not only to avoid leakage of the electrolyte solution from cells and to provide the cells with improved safety but also to achieve higher design tolerances on cell configurations, cell thickness reductions, improvements in durability, and higher outputs owing to increases in area.
The conventional high molecular substances for solidifying electrolyte solutions have crosslinked structures, are insoluble in solvents, and do not melt under heat. Accordingly, they cannot be formed into thin films of uniform thickness. Use of a solid electrolyte in the form of a thin film is indispensable for the construction of a cell of smaller dimensions, especially of a reduced thickness. Because the above-described high molecular substances cannot be formed into thin films, it has heretofore been difficult to obtain a solid electrolyte in the form of a thin film of uniform thickness.
An object of the present invention is, therefore, to provide a solidifying material for a cell electrolyte solution, which can be formed into a thin film or sheet (which may hereinafter be collectively called xe2x80x9cfilmxe2x80x9d) of uniform thickness and can easily absorb and solidify the electrolyte solution.
Another object of the present invention is to provide a cell making use of such a solidifying material.
The above-described objects can be achieved by the present invention as will be described hereinafter.
Described specifically, the present invention, in a first aspect thereof, provides a solidifying material for a cell electrolyte solution, characterized in that the solidifying material is a block copolymer comprising, as segments A, a polymer non-compatible with the cell electrolyte solution and, as segments B, a polymer compatible with the cell electrolyte solution, and absorbs and solidifies the cell electrolyte solution, a smallest unit of the block copolymer is A-B-A, and to each of the segments B, at least one group selected from the group consisting of a carboxyl group, an ester group, a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonate group and a polyoxyalkylene group is bonded via a xe2x80x94Sxe2x80x94 bond or a xe2x80x94Cxe2x80x94 bond; and a cell comprising the solidifying material as a constituent element.
The present invention, in a second aspect thereof, also provides a solidifying material for a cell electrolyte solution, characterized in that the solidifying material is a graft copolymer comprising, as segments A, a polymer non-compatible with the cell electrolyte solution and, as segments B, a polymer compatible with the cell electrolyte solution, and absorbs and solidifies the cell electrolyte solution, and to each of the segments B, at least one group selected from the group consisting of a carboxyl group, an ester group, a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonate group and a polyoxyalkylene group is bonded; and a cell comprising the solidifying material as a constituent element.
The present invention, in a third aspect thereof, also provides a solidifying material for a cell electrolyte solution, characterized in that the solidifying material comprises a film or sheet of a polymer having properties that the polymer is insoluble in the cell electrolyte solution but the polymer absorbs and solidifies the cell electrolyte solution, and a backing reinforcing the film or sheet, and the backing is a woven fabric, a nonwoven fabric or a porous film; and a cell comprising the solidifying material as a constituent element.
The solidifying materials according to the present invention can be dissolved or finely dispersed in appropriate solvents or can be caused to melt by heat, so that they can be formed into films each of which has a desired thickness. Namely, the solidifying materials according to the present invention can be formed into thin films of uniform thickness, and can easily absorb and solidify cell electrolyte solutions. As these films can be provided with enhanced strength by reinforcing them with backings, these films can each be formed with a still reduced thickness. These film-shaped solidifying materials can conveniently absorb and solidify electrolyte solutions, and the thus-solidified electrolyte solutions have good electrical conductivity and are useful as solid electrolytes for cells. Upon absorption of electrolyte solution in each of these films, the volume of the film increases in the direction of its cross-section, in other words, toward an associated electrode, so that the contact between the electrode and the film is rendered closer an surer. Especially when a woven fabric is used as a backing, a reduction in electrical conductivity can be minimized because the woven fabric has adequate strength despite its large opening area and moreover, a solidifying material having a large particle size can also be used for the preparation of a coating formulation which is useful for forming a film.